FIG. 23 is a block diagram of a configuration of a high-frequency heating device which is an example of a high frequency device. This high-frequency heating device 500 includes a high frequency generator 1 serving as a high frequency source that generates microwaves and a heating chamber 6 serving as a high frequency load. The high frequency generator 1 includes, for example, a magnetron being a microwave generator, a power unit, a control circuit, etc. The high frequency generator 1 and the heating chamber 6 are connected through a waveguide 2, which is a transmission path for transmitting high-frequency waves. A circulator 3, a power monitor 4, and a matching unit 5 are sequentially provided on the waveguide 2.
The operation of the high-frequency heating device 500 will be described. The high frequency generator 1 generates microwaves W of 2.4 to 2.5 GHz corresponding to the absorption band of water. The microwaves W are transmitted through the waveguide 2, pass sequentially through the circulator 3, the power monitor 4, and the matching unit 5, and reach the heating chamber 6. The power monitor 4 monitors the intensity of the microwaves W passing therethrough and displays the monitored intensity. The matching unit 5 is used to match the impedance of the waveguide 2 to the impedance of the heating chamber 6.
FIG. 24 is a diagram illustrating the heating of a heating object O in the heating chamber 6 shown in FIG. 23. The heating chamber 6 includes: a turntable 6a on which the heating object O containing water is placed; a stirrer fan 6b for randomly reflecting the microwaves W; and an electric heater 6c for oven heating. In the heating chamber 6, the microwaves W introduced from the waveguide 2 connected to the matching unit 5 are absorbed by the heating object O on the rotating turntable 6a while being reflected by inner walls 6d of the heating chamber 6 and also randomly reflected by the stirrer fan 6b, and the heating object O is thereby heated. In the heating chamber 6, the heating object O can also be oven-heated by applying heat H to the heating object O using the electric heater 6c. 
Microwaves W not used to heat the heating object O in the heating chamber 6 are outputted to the waveguide 2 as reflected microwaves RW having the same frequency as that of the microwaves W. Then, the reflected microwaves RW return through the waveguide 2, pass sequentially through the matching unit 5 and the power monitor 4, and reach the circulator 3, as shown in FIG. 23.
The circulator 3 includes a first port 3a, a second port 3b, and a third port 3c and has the function of outputting the microwaves W inputted from the first port 3a to the second port 3b and outputting the reflected microwaves RW inputted from the second port 3b to the third port 3c. As described above, the circulator 3 has the function of preventing the reflected microwaves RW from returning to the high frequency generator 1 to prevent, for example, damage to and unstable operation of the high frequency generator 1.
A load referred to as a dummy load 7 is connected to the third port 3c of the circulator 3. The dummy load 7 is configured such that the reflected microwaves RW outputted from the third port 3c are absorbed by an absorber to convert the electric power of the reflected microwaves RW to heat, so that the electric power is disposed of as heat. When the electric power of the reflected microwaves RW is high, the amount of heat generated is also large. Therefore, cooling means such as a cooling fan is provided in the dummy load (see Non Patent Literature 1). The circulator to which such a dummy load is connected is widely used not only in high frequency heating devices but also in high frequency devices for particle accelerators and radio communication devices (See Non Patent Literatures 2 and 3).